In the manufacture of corrugated paperboard, a single facer apparatus is used to corrugate the medium web, to apply glue to the flute tips on one face of the corrugated medium web, and to bring a liner web into contact with the glued flute tips of the medium web with the application of sufficient heat and pressure to provide an initial bond. For many years, conventional single facers have typically included a pair of fluted corrugating rolls and a pressure roll, which are aligned so that the axes of all three rolls are generally coplanar. The medium web is fed into a corrugating nip formed by the interengaging corrugating rolls. While the corrugated medium web is still on one of the corrugating rolls, adhesive is applied to the flute tips by a glue roll. The liner web is immediately thereafter brought into contact with the adhesive-coated flute tips.
In the past, the fluted corrugating rolls have typically been generally the same size as each other. More recently, a significantly improved single facer apparatus has been developed in which the corrugating rolls comprise a large diameter bonding roll and a substantially smaller diameter roll, with the ratio of diameters preferably being 3:1 or greater. One such apparatus is disclosed in U.S. Pat. No. 5,628,865, and improvements thereon are described in copending application Ser. Nos. 08/854,953, filed May 13, 1997 and 09/044,516, filed Mar. 19, 1998, and 09/244,904, filed Feb. 4, 1999, all of which disclosures are incorporated herein by reference. In accordance with these disclosures, the single facer typically includes a backing arrangement for the small diameter corrugating roll. One preferred backing arrangement includes a series of axially adjacent pairs of backing idler rollers, each pair having a backing pressure belt entrained therearound. Each of the pressure belts is positioned to bear directly against the fluted surface of the small diameter corrugating roll on the side of the small corrugating roll opposite the corrugating nip. Each pair of associated idler rolls and pressure belts is mounted on a linear actuator, and can thus engage the small diameter corrugating roll with a selectively adjustable force. The application of force against the small diameter corrugating roll, in turn, applies force along the corrugating nip between the small diameter roll and the large diameter roll. Typically, a force of approximately 100 lbs. per linear inch (e.g. 10,000 lbs. for a 100 inch roll) is desirable for properly fluting a medium web at typical line speeds.
The impact of the flutes on the small diameter corrugating roll against the flutes on the large diameter corrugating roll along the corrugating nip can cause undesirable vibrations that can detriment the quality of corrugation. More specifically, chordal action due to the interengagement of the rolls causes the small diameter roll to move up and down. The center axis of the large diameter roll is analytically stationary, and vibrational energy is transmitted primarily to the small diameter roll and to the belted backing arrangement. It has been found that excessive vibrations of the belted backing arrangements is sometimes evident under certain high-speed operating conditions, especially when the system is operated at or near the natural resonance frequency of the system.